U.S. patent application number 10/950958 was filed with the patent office on 2006-03-30 for triband passive signal receptor network.
This patent application is currently assigned to Sawtek, Inc.. Invention is credited to Benjamin P. Abbott, Wang-Chang Albert Gu, Berry Leonard, Riad Mahbub, Rushad Mehershahi.
Application Number | 20060067254 10/950958 |
Document ID | / |
Family ID | 36098943 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060067254 |
Kind Code |
A1 |
Mahbub; Riad ; et
al. |
March 30, 2006 |
Triband passive signal receptor network
Abstract
A surface acoustic wave (SAW) triplexer receives radio frequency
signals in three bands and provides output signal components for
PCS, GPS, and cellular signal processing ports. The triplexer
includes low pass filter and a high pass network operating with an
antenna terminal for reception and separation of an incoming signal
in a low and high frequency bands, and a SAW filter connected to
the input terminal for reception and separation of the incoming
signal within a frequency band located between that of the low and
the high bands. A low insertion loss bandpass filter is provided by
the SAW filter having a transducer and reflectors fabricated on a
piezoelectric substrate.
Inventors: |
Mahbub; Riad; (Apopka,
FL) ; Leonard; Berry; (Apopka, FL) ; Gu;
Wang-Chang Albert; (Longwood, FL) ; Mehershahi;
Rushad; (Orlando, FL) ; Abbott; Benjamin P.;
(Longwood, FL) |
Correspondence
Address: |
CARL M. NAPOLITANO, PH.D.;ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST, P.A.
255 SOUTH ORANGE AVE., SUITE 1401
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
Sawtek, Inc.
Orlando
FL
|
Family ID: |
36098943 |
Appl. No.: |
10/950958 |
Filed: |
September 27, 2004 |
Current U.S.
Class: |
370/282 ;
333/133; 370/293; 455/324 |
Current CPC
Class: |
H04B 1/0057 20130101;
H03H 9/72 20130101; H03H 9/725 20130101; H04B 1/0053 20130101; H03H
9/0576 20130101 |
Class at
Publication: |
370/282 ;
370/293; 333/133; 455/324 |
International
Class: |
H03H 9/00 20060101
H03H009/00; H04B 1/44 20060101 H04B001/44; H04B 3/36 20060101
H04B003/36; H01L 41/00 20060101 H01L041/00 |
Claims
1. A surface acoustic wave (SAW) triplexer useful in receiving
radio frequency signals in at least three bands and providing
output signal components to signal processing ports, the triplexer
comprising: a low pass filter network suitable for operating with
an input terminal for reception and separation of an incoming
signal in a low frequency band; a high pass filter network operable
with the input terminal for reception and separation of the
incoming signal in a high frequency band; and a surface acoustic
wave (SAW) filter for connecting to the input terminal for
reception and separation of the incoming signal at a frequency band
located between that of the low and the high bands of the signal,
wherein the SAW filter comprises at least one transducer and
reflectors fabricated on a piezoelectric substrate for providing a
low insertion loss bandpass filter.
2. The triplexer according to claim 1, wherein at least one of the
low pass, high pass, and SAW filters is connected to the input
terminal through a phase matching network.
3. The triplexer according to claim 1, wherein a characteristic of
the low pass filter network includes an impedance close to a system
characteristic impedance at the low frequency band, and an
impedance at the low frequency band of the SAW filter is inductive
while the impedance at the low frequency band for the high pass
filter network is capacitive.
4. The triplexer according to claim 1, wherein the impedance at a
center frequency of the SAW bandpass filter network is close to a
system characteristic impedance within which the triplexer is
operable and an out of band impedance at the low frequency band is
inductive and the impedance at the high frequency band is
capacitive.
5. The triplexer according to claim 1, wherein a rejection of the
SAW bandpass filter at the frequency band of the high pass filter
is greater than 25 dB.
6. The triplexer according to claim 1, wherein a minimum insertion
loss of the low pass filter, the SAW bandpass filter, and the high
pass filter is less than 2.0 dB.
7. The triplexer according to claim 1, wherein the triplexer is
operable with a concurrent reception and transmission of different
signal bands.
8. A surface acoustic wave (SAW) triplexer comprising: an input
terminal providing an incoming signal; a low pass filter network
connected to the input terminal for reception and separation of the
incoming signal of a low frequency band having signal components
within a frequency band of 824 MHz to 894 MHz; a high pass filter
network connected to the input terminal for reception and
separation of the incoming signal of a high frequency band with
signal components within a frequency band of 1850 to 1990 MHz; and
a surface acoustic wave (SAW) filter which connected to the input
terminal for reception and separation of the incoming signal at a
frequency band with signal components within 1570 to 1580 MHz,
wherein the SAW filter comprises a transducer and reflector
fabricated on a piezoelectric substrate for providing a low
insertion loss bandpass filter.
9. The SAW triplexer according to claim 6, wherein a minimum
insertion at each of the bands is less than 2.0 dB and a rejection
of the SAW bandpass filter at the frequency band ranging from 1850
MHz to 1990 MHz is greater than 25 dB.
10. The SAW triplexer according to claim 6, wherein an impedance of
the SAW bandpass filter at about 1575 MHz is approximately 50 ohms,
an impedance at the frequency band of 824 MHz to 894 MHz is
inductive, and at the frequency band of 1850 to 1990 MHz is
capacitive.
11. The SAW triplexer according to claim 6, wherein reception and
transmission of the band signals is simultaneous.
12. A triplexer comprising: an input terminal for providing an
incoming signal; a low pass filter network connected to the input
terminal for receiving and separating the incoming signal into a
low frequency band; a high pass filter network connected to the
input terminal for receiving and separating the incoming signal
into a high frequency band; and a surface acoustic wave (SAW)
filter connected to the input terminal for receiving and separating
the incoming signal at a frequency band located between the low and
the high frequency bands.
13. The triplexer according to claim 12, further comprising a
parallel tank circuit operable within the low pass filter network
and a series tank circuit operable within the high pass filter
network, the tank circuits operable for providing a notching for
undesirable frequencies components.
14. The triplexer according to claim 12, wherein the SAW filter
comprises a longitudinal coupled resonator.
15. The triplexer according to claim 14, wherein the resonator
comprises an input transducer and two output transducers connected
in parallel thereto, wherein the output transducers are embedded
between reflectors for forming multiple resonances coupling with
each other for providing a low loss bandpass filter.
16. The triplexer according to claim 12, wherein a characteristic
of the low pass filter network includes an impedance close to a
system characteristic impedance at the low frequency band, and an
impedance at the low frequency band of the SAW filter is inductive
while the impedance at the low frequency band for the high pass
filter network is capacitive.
17. The triplexer according to claim 12, wherein the impedance at a
center frequency of the SAW bandpass filter network is close to a
system characteristic impedance within which the triplexer is
operable and an out of band impedance at the low frequency band is
inductive and the impedance at the high frequency band is
capacitive.
18. The triplexer according to claim 12, wherein a rejection of the
SAW bandpass filter at the frequency band of the high pass filter
is greater than 25 dB.
19. The triplexer according to claim 12, wherein a minimum
insertion loss of the low pass filter, the SAW bandpass filter, and
the high pass filter is less than 2.0 dB.
20. The triplexer according to claim 12, wherein the triplexer is
operable with a simultaneous reception and transmission of
different signal bands.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to wireless
communication systems and more particularly to a multiple frequency
band passive signal receptor network.
BACKGROUND OF THE INVENTION
[0002] Dual Band Mobile Phones covering both the Code Division
Multiplex Access (CDMA) cellular and the Personal Communication
Systems (PCS) bands have been in common use for quite sometime. The
cellular band operates in the frequency range from 824-894 MHz
while the PCS band covers the higher frequency band of 1850-1990
MHz. Recently, the addition of global position system (GPS) to the
mobile phone has significantly enhanced its functionality to
provide positioning information with regards to the handset through
a systematic network of base-stations and satellites. The GPS
operates in a narrow frequency band with center frequency around
1575 MHz. The integration of a GPS function adds a new dimension of
complexity to the phone design. One of the requirements of a
tri-band phone design is a network that can receive an incoming
signal and provide signal separation of three distinctive bands
without any significant degradation of signal fidelity.
[0003] Various architectures are being implemented in mobile
handsets. As illustrated with reference to FIG. 1, by way of
example, signal reception networks that incorporates two antennas
are well known. Typically, one antenna is tuned for receiving the
cellular and PCS bands of frequencies while a second antenna is set
for the reception of the GPS signal only. With the desired
reduction in phone size, a proper placement of two antennas poses a
complicated issue. Such an approach has significant performance and
size limitations and hence there is a need to provide a single
antenna approach.
[0004] A known alternative signal reception network incorporates
the use of a two-way switch, as illustrated with reference to FIG.
2. One output of the switch is connected to a diplexer that
separates the cellular band from the PCS band signals. The other
output of the switch is connected to a bandpass filter covering the
GPS frequency band. Yet another switch antenna signal reception
network is a three-way switch approach that has three dedicated
outputs for the cellular, PCS and GPS frequency bands. However,
such switch styled solutions have their drawbacks. The two-throw
switch/diplexer solution, illustrated with reference to FIG. 2, has
a performance degradation issue because of a cascading of insertion
losses of the switch and the diplexer in the critical cellular and
PCS frequency bands. On the other hand, the three throw switched
solution provides low insertion loss. However, its poor
cross-modulation performance is a great concern to phone system
design engineers. Both the switched solutions need control lines
for the operation of the switches that are generally comprised of
PIN or PHEMT diodes. Additional DC blocking capacitors required at
the RF ports and bypass capacitors at the control lines typically
increase the cost and size of the mobile handset. Typically, a
switch may exhibit a further disadvantage in that only a single
band is activated at any instant of time. Concurrent reception and
transmission of signal components from different bands is not
possible.
[0005] Hence, it is desirable to have a signal reception network
that is passive, requiring no control lines, and able to provide
good performance in insertion and rejection, while at the same time
meet the small size and cost requirements. It is also desirable to
have a signal reception network that can provide simultaneous
receive and transmit functionality of the different signal
bands.
SUMMARY OF THE INVENTION
[0006] The present invention provides embodiments including a
passive signal reception network that can receive and separate a
frequency signal into distinct bands. One embodiment includes
triplexer having at least a low loss Surface Acoustic Wave (SAW)
bandpass filter, a low pass filter and a high pass LC filter
forming a passive network that can receive and appropriately
separate the signal into three different distinct bands. Another
embodiment includes a passive SAW triplexer including a low pass
and high pass filtering network connected to an antenna directly or
through matching or phasing network for reception and separation of
the signal. The triplexer may be optimized to provide low insertion
loss for each appropriate receiving signal and maintains
substantial attenuation and isolation for the other signals that
may be out of band frequency signals. The present invention also
provides a SAW triplexer that enables simultaneous reception and
transmission of different signal bands.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Embodiment of the present invention are herein described by
way of example with reference to the accompanying drawings in
which:
[0008] FIG. 1 is a block diagram illustrating a dual antenna signal
reception network known in the art;
[0009] FIG. 2 is a block diagram illustrating an active signal
reception network known in the art;
[0010] FIG. 3 is a block diagram illustrating a passive signal
reception SAW triplexer of the present invention
[0011] FIG. 4 is partial plan view of a three-transducer coupled
resonator filter;
[0012] FIG. 5 is a schematic layout of a ladder filter;
[0013] FIG. 6 is a diagrammatical view of a SAW single pole
resonator and equivalent schematics:
[0014] FIG. 7 is a schematic of a SAW triplexer of the present
invention;
[0015] FIG. 8 is a plot illustrating impedance characteristics of a
cellular network;
[0016] FIG. 9 is a plot illustrating impedance characteristics of a
personal communications service (PCS) network;
[0017] FIG. 10 is a plot illustrating impedance characteristics of
a global positioning system (GPS) network;
[0018] FIG. 11 illustrates a frequency response of a low pass
filter;
[0019] FIG. 12 illustrates a frequency response of a SAW bandpass
filter;
[0020] FIG. 13 illustrates a frequency response of a high pass
filter; and
[0021] FIG. 14 is a partial perspective view of a triplexer
assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout, and prime notation is used to indicate similar
elements in alternate embodiments.
[0023] Referring initially to FIG. 3, one embodiment of the present
invention includes a SAW triplexer 10, herein illustrated in a
block diagram including a SAW bandpass filter 12, a low pass filter
14, and a high pass filter 16 connected directly or indirectly
through a phase matching network, which may be located at point 18,
to a single antenna 20 for providing signal reception and
separation. The low loss SAW bandpass filter 12 covers the GPS
frequency band with center frequency around 1575 MHz. The low pass
filter 14 receives and separates the cellular band signal
frequencies from 824 to 894 MHz, while the high pass filter 16 only
allows passage of the PCS frequency band of 1850 to 1990 MHz. Thus,
the low pass filter 14 provides a path for the lower frequency
components of the signal, while the high pass filter 16 provides
the path for the highest frequency band of interest and the mid
band signal component is extracted with the help of the SAW
bandpass filter 12. Once the signal component is separated, it is
then sent to its appropriate port, PCS 22, GPS 24, and cellular 26,
for further processing.
[0024] By way of example, the SAW bandpass filter 12 may be a
coupled resonator filter (CRF) or a ladder type filter. One coupled
resonator SAW filter 28 including three transducers 30, 32, 34
arranged in a side-by-side manner along a longitudinal axis 36 and
embedded between the two reflectors 38, 40, is illustrated by way
of example with reference to FIG. 4. The transducers and reflectors
may be fabricated on a piezoelectric substrate 42 of Lithium
Tantalate or Lithium Niobate. The electrode fingers 44 of the
transducers 30, 32, 34 and reflectors 38, 40 may be composed of
Aluminum metal or Aluminum alloys. The coupled resonator SAW filter
28 is one preferred filter because it exhibits very low insertion
loss yet provides a very good out-of-band rejection.
[0025] Another SAW bandpass filter 12 that may be used in an
embodiment of the triplexer 10, above described, is a SAW ladder
filter 46, as illustrated by way of example with reference to FIG.
5. As herein described, the SAW ladder filter 46 may comprise a
single pole SAW resonator 48 arranged in either the series arm 50
or the parallel arm 52 for forming a ladder network. The SAW single
pole resonator 48, as herein described by way of example, and its
equivalent schematic 54 are illustrated with reference to FIG. 5.
The resonator 48 may include a single transducer 30 embedded
between the two reflectors 38, 40. Both these types of SAW filters
are well known to those skilled in the art.
[0026] With reference now to FIG. 7, one embodiment of the SAW
triplexer 10 is herein illustrated in schematic form by way of
example. The low-pass filter 14 and the high-pass filter 16 as
herein described may be fabricated with inductive and capacitive
(LC) components, as illustrated with L.sub.1 and C.sub.1 for the
low pass filter and L.sub.2, C.sub.2, and C.sub.3 for the high pass
filter. A parallel tank circuit 56 at the low-pass filter branch
(L.sub.P and C.sub.P) and a series tank circuit 58 at the high-pass
filter network (L.sub.2 and C.sub.S) provide a strategic "notching"
of undesirable frequencies components. The inductor 60 connected
from the input 62 to ground 64 provides phasing and impedance
matching for the triplexer 10.
[0027] The triplexer 10 receives a signal from the antenna 20 and
separates its frequency components with minimum loss degradation
while able to maintain high signal component fidelity. It provides
significant isolation between each of the three frequency bands as
above described for the PCS, GPS, and cellular. Thus, the SAW
bandpass filter 12, which has a passband of about 10 to 20 MHz,
while receiving the GPS frequency component with minimum insertion
loss provides substantial attenuation for the cellular and PCS
frequency components. These criteria present a critical challenge
in the integration of filter networks. Simply incorporating the SAW
filter 12 with the low pass and high pass filters 14,16, may allow
impedance and phase mismatch to degrade the signal passband. Due to
impedance mismatch, reflections from each of the network paths
interfere with each other thereby reducing the isolation between
each of the three frequency bands. Integration of the filter
networks thus requires a stringent phase and impedance matching to
ensure signal fidelity and good isolation.
[0028] The SAW triplexer 10 uses a very high rejection GPS SAW to
improve single tone desensitization performance of the cellular
telephone (phone). Single tone desensitization is a measure of the
handset's ability to receive a CDMA PCS signal in the presence of a
single jamming tone spaced at a given frequency offset from the
CDMA signal's center frequency. The single tone desensitization of
a phone is affected by a third order inter-modulation product of a
low-noise amplifier (LNA) and receiver rejection at a transmitter
band of the duplexer. Additionally, the suppression of leakage of
power through GPS path is also desirable, especially for those
telephone layouts in which the components are so physically close
together. The GPS SAW with high rejection at PCS band is thus
desirable for the SAW triplexer 10.
[0029] Optimized triplexer performance is provided. With reference
now to FIGS. 8, 9, and 10, illustrating impedance/admittance
characteristics of the Cellular, PCS and GPS networks,
respectively. With reference to FIG. 8, in a cellular network the
in-band impedance at m1 is matched closely to 50 ohms
(characteristic impedance of one system, by way of example), while
the out-of-band impedances at m2 and m3 are maintained very
inductive and at relatively high frequency values. For the PCS path
(see FIG. 9), as before, the impedance at the center of the PCS
band at m5 is set to be about 50 ohms while its out-of-band
impedances at m6 and m4 are capacitive. Similarly, for the GPS path
(see FIG. 10), the impedance at the GPS center frequency m9 of 1575
MHz is designed to be close to 50 ohms, while its out of band
cellular and PCS impedances at m7 and m8 are set away from the
characteristics impedance of 50 ohm with m8 being capacitive and m7
inductive. By way of example, at the cellular path, a signal with a
cellular frequency component will realize minimal mismatch since
impedance at about the center of the low frequency band (m1) is
closely matched to the system characteristic impedance of 50 ohms
and the impedance at the same low frequency band of the high-pass
filter network (m4) being capacitive would cancel with the
inductive component of the SAW bandpass filter at the low frequency
band(m7). The impedances at m4 and m7 may be targeted to be as
close to complex conjugates as possible which assist in impedance
cancellation. This would minimize reflections at the passband
frequencies arising from other filter sections, thereby enhancing
the isolation characteristics of the triplexer 10. To ensure low
insertion loss performance, the out-of-band impedances are designed
in such a way that the parallel combination of any two out-of-band
impedances at a specific frequency band provides very high
impedance. Thus, when the high impedance is in parallel to the
in-band impedance, the equivalent impedance remains very close to
that of the in-band impedance. This reduces mismatch loss and thus
ensures low insertion loss performance of the triplexer 10. Yet
further, greater rejection of the out-o- band frequencies is
enhanced by the incorporation of the series and parallel tank
circuits 58, 56 in the high pass and low pass filters 16, 14 as
earlier described with reference to FIG. 7.
[0030] Frequency responses for each of the filter sections,
cellular 26, GPS 24, and PCS 26 of the triplexer 10 are illustrated
with reference to FIGS. 11,12, and 13, for the low pass 14, SAW
bandpass 12, and high pass 16 filters respectively. With continued
reference to FIG. 11, the low pass filter 14 exhibits very low loss
at the desired frequency band of 824 MHz-894 MHz, while it rejects
the GPS and PCS frequency bands. The insertion loss across the
desired low frequency band is typically less than 1.0 dB. A notched
frequency at around the GPS frequency band is realized by the tank
circuit 56 incorporated in the low-pass filter 14 portion of the
triplexer 10, earlier described with reference to FIG. 7.
Similarly, the high-pass filter 16 provides low insertion loss
(typically less than 1 dB) for PCS frequency band and rejects the
GPS and cellular band signal components, as illustrated with
reference to FIG. 13. As the GPS frequency band is very close to
the PCS band, it is necessary that a notched frequency be set at
about the GPS frequency with the help of the resonance tank circuit
58 in the high pass filter 16 network earlier described with
reference to FIG. 7. The frequency plot of the high pass filter
clearly shows a GPS notched frequency at about 1575 MHz. This is
accomplished with the series tank circuit 58 in the high pass
filter 16 section of the triplexer 10.
[0031] As herein described by way of example, the SAW bandpass
filter 12 may be the longitudinal coupled resonator 28 earlier
described with reference to FIG. 4. The SAW resonator,28 has an
input transducer 30 and two parallel connected output transducers
32, 34 embedded between the reflectors 38, 40 forming multiple
resonances that can couple with each other for providing a low loss
bandpass filter. The insertion loss of the filter 28 is less than
1.5 dB while the rejections at the cellular frequency band and PCS
band is greater than 25 dB. The high out of band rejection at the
high-pass filter frequencies as achieved by the SAW bandpass filter
is very desirable for providing better isolation. The bandpass
filter 28 has a dimension of 2.5 mm.times.2.1 mm.times.1.5 mm. SAW
filters thus provide excellent loss and very good close in
rejection in a very small size.
[0032] One embodiment of the triplexer 10 including components as
above described and in keeping with the teachings of the present
invention is illustrated with reference to FIG. 14. Ceramic chip
capacitors 66, inductors 68, and the SAW bandpass filter 12 are
mounted on a direct printed copper base substrate 70. However, any
organic or ceramic substrate may be used for the printed circuit
substrate where passives may be embedded or integrated in the
substrate. While chip inductors 68 and capacitors 66 are used in
the example of the embodiment, any type of reasonably high Q
inductor or capacitor may be used. The assembly of components may
be sealed with a lid 72 to facilitate further integration of the
triplexer 10 into a mobile phone system. The lid 72 may take any
form including, but not limited to, a metal lid or plastic
over-mold compound. However, it will be understood by those skilled
in the art that a lid may not be needed for all applications. By
way of further example, size reduction may be achieved by embedding
some of the inductors and capacitors within a Low Temperature
Co-fired Ceramic (LTCC) substrate or through integration involving
other substrate technologies.
[0033] Many modifications and other embodiments of the invention
will come to the mind of one skilled in the art having the benefit
of the teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is understood that the invention
is not to be limited to the specific embodiments disclosed, and
that modifications and embodiments are intended to be included
within the scope of the appended claims.
* * * * *